1. Field of the Invention
This invention relates generally to a feedthrough circuit assembly and a method for providing a conductor of electrical current through a conductive wall or enclosure. More particularly, this invention relates to a 0.060 inch current feedthrough having a 0.040 inch diameter center conductor that is brazed to an insulating material for providing electrical conduction through the insulating material.
2. Brief Description of the Art
The prior art is replete with various means and methods for providing electrical conduction between semiconductor devices. A prior art method for providing an electrical pass or feedthrough connection between opposing sides of a conductive wall typically uses a glass insulating material disposed in a through-bore formed in the wall. The glass insulating material covers the feedthrough conductor and thereby insulates the conductor from the wall of an equipment housing or other walled enclosure through which the conductor passes.
U.S. Pat. No. 4,292,464, issued Sep. 29, 1981 to Vogt et al., discloses a glass pass-through with an additional insulator for a lengthening a leakage path. This pass-through has a glass part disposed in an opening formed in a metal case. The insulator for lengthening the leakage path is connected to one end of the glass part and to an electric conductor. The connection between the insulator and the glass part includes a fused glass junction.
U.S. Pat. No. 5,194,697, issued Mar. 16, 1993 to Hegner et al., discloses an electrically conductive feedthrough connection. A mechanically heavily loadable and high-vacuum-tight feedthrough is connected through a hole in a high temperature-resistant and vacuum-proof insulating portion that could be ceramic, glass or a single crystal. The feedthrough circuit is disclosed as preferably used in a capacitive pressure sensor having a diaphragm and a substrate.
U.S. Pat. No. 4,935,583, issued Jun. 19, 1990 to Kyle, discloses an insulated conductor with ceramic-connected elements. An electrical conductor that has a particular coefficient of thermal expansion is bonded to an electrical insulator having a relatively similar coefficient of thermal expansion. The bonding material is a ceramic material having a similar coefficient of thermal expansion as the electrical insulator. The bonding is accomplished by disposing the ceramic material between the electrical conductor and the electrical insulator and by subjecting the ceramic material to a controlled amount of heat, which may be applied by a laser beam. The heat created by the laser causes the ceramic material to flow in the space between the electrical conductor and the electrical insulator, thereby bonding the electrical conductor and the electrical insulator.
U.S. Pat. No. 5,539,611, issued Jul. 23, 1996 to Hegner et al., discloses an interface connection through an insulating part. This interface connection is through a hole in a high temperature-resistant and vacuum-proof insulating part, and consists of a metallic lead inserted into the hole and having a coefficient of thermal expansion less than that of the insulating part. One end of the lead is flush with a surface of the insulating part and is covered with an active brazing material, which seals it to the insulating part.
U.S. Pat. No. 3,901,772, issued Aug. 26, 1975 to Guillotin et al., discloses a method of sealing of a metal part on a ceramic part by brazing. This method creates a fluid-tight sealing joint between a metal part and a ceramic material. The ceramic part is metallized by the application of a metallization product containing a metallic derivative, and sintering the product. The ceramic part is then nickel coated. This method requires repeated coatings of metallization and two nickel layers.
As can be seen from the illustrative background discussed above, there is a need for a method and apparatus that enables a conductor having a varying diameter to provide a current path through a ceramic insulating material. As increased power is required in semiconductor devices, larger diameter leads are required and/or leads with lower resistance. Standard package sizes and external lead diameter are fixed by industry and government standards. Packages with 0.060 inch diameter external leads have become standards, but are not capable of being produced with low resistance materials. The mismatch in thermal expansion between the external lead and the ceramic material to which the lead is joined becomes problematical as the external lead approaches 0.060 inches in diameter. This mismatch in thermal expansion can cause a failure in the joint, the lead, or the ceramic material.